Diverse ink jetting processes have been developed for the recording method by means of ink-jet printer, and any process comprises generating ink droplets to deposit them onto various recording materials (such as paper, film, cloth) for recording. The recording method by means of ink-jet printer is characterized by generating no sound, thus being silent and being able to print character on rough surface, soft material, fragile products and the like in any place due to the system in which a recording head does not contact with the recording material and the method has rapidly been spread in recent years and will be propagated in future because the method advantageously allows the printer to become downsized, to work in a high-speed and to give color printing, easily. For recording an image information or a character information pictured on a computer color display in color by means of an ink-jet printer, the information is generally printed according to subtractive color mixing of inks of four colors, namely black (K) plus trichromatic color of yellow(Y), magenta(M) and cyan(C). In order to print reproductively an image pictured by additive color mixing of R(red), G(green), B(blue) on a CRT display as faithfully as possible according to subtractive color mixing, the dyestuffs used, especially ones for a YMC ink, are desired to have color hues close to the respective standards of YMC and vividness. Additionally, it is required that the resulting ink composition is stable for long-term storage and that the resulting printed image is of a high optical density and has excellent fastness including water fastness and light fastness. Where the ink composition is applied to displays such as advertisements to spread the usable fields, the printed articles increases opportunities to be exposed to light (electric light, fluorescent light, sun light and the like). Hence, a demand exists for an ink composition particularly excellent in light fastness.
Many of the cyan ink compositions employ phthalocyanine dyes such as C. I. Direct Blue 86 or C. I. Direct Blue 199, which has higher light fastness than those of magenta and yellow dyes. Unfortunately, if a commonly used phthalocyanine dye such as C. I. Direct Blue 86 or C. I. Direct Blue 199 is used for printing a coated paper generally called glossy paper and then the resultant print is allowed to stand in a well ventilated shade for a long time (hereinafter referred to as “exposure to weather”), the print is soon discolored or faded. Although an exact cause is not known, the discoloration of the dye seems to be induced by interaction between ozone gas in the atmosphere and an inorganic substance and/or a polymer applied to the coated paper. The cyan dye suffers the greatest degree of discoloration, having the lowest level of color fastness. For this reason, water-based cyan ink compositions have not been yet provided as products to fully satisfy the market demand.
The application of the ink-jet printers has been extended from compact printers for office automation to large printers for industrial use. Accordingly, the prints produced by these printers are more likely to be exposed to outside weather so that higher water fastness and light fastness than ever are required. The water fastness may be notably improved by coating inorganic fine particles capable of adsorbing dye particles in ink, such as of silica, a cationic polymer, alumina or a ceramic with a PVA resin on a paper surface. A phthalocyanine dye for cyan is superior to other magenta and yellow dyes in light fastness and hence, is not studied so much as magenta and yellow dyes to improve the light fastness. However, the cyan dye used in the art is discolored or faded if it is used to print the coated paper which is called the glossy paper and then the resultant print is allowed to stand under exposure to weather or ozone gas. To overcome this problem, after printed the prints are laminated for suppressing the discoloration. However, this method has large problems in terms of time efficiency, convenience and cost. As a fundamental solution to these problems, it is an important object to develop a cyan dye which is less susceptible to discoloration under exposure to weather or ozone gas.
A typical skeleton of the cyan dye for use in the water-based ink composition for ink-jet recording is a triphenylmethane series or a phthalocyanine series. Triphenylmethane dyes exhibit favorable hues but are seriously inferior in water fastness and light fastness. In addition, there is a problem that the dyes, after printed on the glossy paper, are discolored or faded under exposure to weather or ozone gas.
On the other hand, the phthalocyanine dyes used in the art are superior in hue, water fastness and light fastness but have a problem that the dyes, after printed on the glossy paper, are discolored or faded under exposure to weather or ozone gas.
It is an object of the invention to provide a cyan ink composition having a color, hue and vividness suitable for ink-jet recording, providing a print excellent in light fastness and water fastness, and suffering less discoloration under exposure to weather or ozone gas after printed on the glossy paper.
The inventors have examined C. I. Direct Blues 199 synthesized under different conditions thereby finally obtained a cyan dye mixture and a cyan ink composition less prone to discolor or fade under exposure to weather or ozone gas after printed on the glossy paper. Thus was accomplished the invention.